Today I performed a quick, dirty and non-scientific test for a highline article I am writing, and I came across some results that may interest climbers. There is a lot of talk about how a short fall on a Dyneema sling can cause the sling to fail, but drop testing fabrics can be a bit abstract, and it can be hard to visualize what is actually going on within the sling during a fall. This quick and dirty test may help make it easier to visualize a shockloading scenario from the viewpoint of the sling.

In the photo below you can see a load cell connected to a bolt and to a 1” nylon webbing sling tied in a sliding X. Attached to the sling is a steel ring that weighs 12 lbs. I picked the ring up and dropped it 20” onto the cell.

The scan rate of my dynometer was actually too slow, and so the dynometer was not able to capture the true peak. Therefore, the actual peak load of this fall is actually slightly higher than what the dyno measured. If you look closely at the graph you will notice that top of the peak is flat. The start and end points of the flat section of the peak is actually the duration between two individual samples!

To further emphasize the short duration of a static fall like what I tested, let us compare it to the graph below. The graph below represents three lead falls in a typical climbing scenario. The load cell was placed on the protection bolt.

The fall above had a duration of around 2,500ms which is obviously far longer than the 24ms the static fall drop test took.

In conclusion, this quick test, which involved a 20” fall of a 12 lb. steel weight, produced a peak load increase of over 3,800%. Although this test is not analogous of a typical climbing shockloading fall due to a lack of a fleshy mass, it still emphasizes how relatively short falls on static materials can produces insane peak loads. I suspect that if the load weighed 80kg, I would have broken the bolt in the ceiling and exceeded the weight limitation of my load cell.

One thing that these shock load tests never take into account is the deformation of the human body during falls. When a harnessed climber falls onto a sling, the shock load will be lessened by the harness digging the climber as well as the jerking of the climbers limbs and torso. So, while the high elastic modulus of sling material is likely to contribute to failure in lab tests with iron weights, actual climbing (where the viscoelasticity of the human body further dampens the load) generally doesn't result in lethal shock loads.

So, even a fall factor 2 on your dyneema sling is very unlikely to damage your sling. Having said that, the shock load will still be unpleasant.

Also, I realize that this isn't completely related to your post, but I've never heard anybody else make this point and I think it needs to be factored into the discussion.

One thing that these shock load tests never take into account is the deformation of the human body during falls.

I noted that in the second to last sentence of my post. I said, "Although this test is not analogous of a typical climbing shockloading fall due to a lack of a fleshy mass, it still emphasizes how relatively short falls on static materials can produces insane peak loads."

One thing that these shock load tests never take into account is the deformation of the human body during falls. When a harnessed climber falls onto a sling, the shock load will be lessened by the harness digging the climber as well as the jerking of the climbers limbs and torso. So, while the high elastic modulus of sling material is likely to contribute to failure in lab tests with iron weights, actual climbing (where the viscoelasticity of the human body further dampens the load) generally doesn't result in lethal shock loads. So, even a fall factor 2 on your dyneema sling is very unlikely to damage your sling. Having said that, the shock load will still be unpleasant. Also, I realize that this isn't completely related to your post, but I've never heard anybody else make this point and I think it needs to be factored into the discussion.

For some reason climbers seem to think the equipment industry is full of unimaginative people, that testing laboratories just get any old weight and drop it and that the people who write the standards just scribble them down on a beer mat one evening.

The standard 80kg used for rope drop tests is a rounded-up mass representing a 100kg mountaineer (not an anorexic sport climber)and has already the soft-body factor included. This was established decades ago after comparative tests with both weights and human volunteers by Troll (the pioneers of sit harnesses) and data from other fields. For good background information on the derivation of human surrogate testing in fall arrest this pdf covers most of the relevant factors hse.gov.uk/research/crr_htm/20....

A FF2 onto a dyneema sling is extremely likely to break something as we know from an accident and the subsequent investigation involving a number of quickdraws which was done a few years ago by one of the major Euro gear manufacturers.